Porosity Estimation from Compressional Wave Velocity： A Study Based on Egyptian Carbonate Samples

The porosity of a rock is one of the most important reservoir properties. It controls the reservoir storage capacity. In other words, porosity quantifies the amount of fluids that the rock can store. Most of the world＇s giant fields produce hydrocarbons from carbonate reservoirs. Carbonate rocks contain more than 50% of the world＇s hydrocarbon reserves. Porosity and compressional wave velocity of 41 carbonate samples were determined under ambient conditions in laboratory. The samples were collected from seven shallow wells in west Tushka area, south Western Desert, Egypt. This paper evaluates the well known Wyllie and Raymer equations, an empirical linear equation, and a generalized model for porosity estimation from compressional wave velocity of saturated carbonate samples. Based on the comparison of the predicting identified to provide the most reliable porosity estimation. qualities, the Raymer equation and the empirical linear equation were

Compressional Wave Velocities in Some Volcanic Rocks at Pressure up to 4.5 GPa

Compressional wave velocities in some Mesozoic and Cenozoic volcanic rocks from Qinling Dabie orogenic belt were measured at room temperature and high pressure (up to 4.5 GPa). Compressional wave velocities of these rocks increase with the increasing of pressure. The experiment data indicate that the pressure at which the microcracks in these rocks finally close is up to 2.0 GPa. The empirical relationships between compressional wave velocities at high pressure and oxide mass fractions, heat productions and densities at room temperature and 100 kPa of these rocks are discussed. It is likely that there does not always exist linear relationship between compressional wave velocities and oxide mass fractions. New heat production data of volcanic rock samples from the Qinling Dabie orogenic belt do not follow the empirical relationship between heat production and seismic velocity for rocks. It is dangerous to use these empirical relations to predicate the modal chemical composition, density and heat production of the lithosphere.

Compressional elastic wave velocities of serpentinized pyroxenite at high pressures and high temperatures and its geological significance

Center for Analysis and Prediction, China Seismological Bureau, Beijing 100036, China 2) Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China

THE INTERACTION BETWEEN SHOCK WAVES AND FOAM IN A SHOCK TUBE

An experimental study and a numerical simulation were conducted to investigate the mechanical and thermodynamic processes involved in the interaction between shock waves and low density foam. The experiment was done in a stainless shock tube (80 mm in inner diameter, 10 mm in wall thickness and 5 360 mm in length). The velocities of the incident and reflected compression waves in the foam were measured by using piezo-ceramic pressure sensors. The end-wall peak pressure behind the reflected wave in the foam was measured by using a crystal piezoelectric sensor. It is suggested that the high end-wall pressure may be caused by a rapid contact between the foam and the end-wall surface. Both open-cell and closed-cell foams with different length and density were tested. Through comparing the numerical and experimental end-wall pressure, the permeability coefficients α and β are quantitatively determined.

Temporal vP/vS variation characteristics in different zones of China's Capital Circle area before and after Wen'an earthquake

On July 4, 2006, an earthquake of MS5.1 took place in Wen’an, Hebei Province, just at the south center of China’s Capital Circle area digital seismograph network. It is the strongest event recorded ever since the network went into operation in 2002. We processed the vast amounts of phase data yielded by the 107 digital seismic stations between 2002~2007 using Wadati method. In order to improve the precision and stability of shear and compressional wave velocities (vP/vS) calculation, we impose a number of restrictions on the computation environment and condition, e.g., the earthquakes are densely concentrated, selected stations are limited in range, the number of stations in- volved in the computation is larger than 5 and linear fitting features high precision and small error. Under these restrictions, the study shows that vP/vS in and around Wen’an and Tangshan underwent a normal-low-normal proc- ess one year before Wen’an earthquake, vP/vS became obviously low and the low ratio lasted for about one year, meanwhile, little variation of vP/vS was seen in Xingtai, northwest of Beijing, southwest of Beijing, Beijing-Tianjin and Beijing; after the quake, the vP/vS returned normal in Wen’an and Tangshan. Error and stability analysis of the calculated result for vP/vS shows it is convincible that anomaly appeared in and around Wen’an and Tangshan be- fore Wen’an earthquake.

Studying of Physical-Mechanical Properties of Rocks of Geological Section Considering the Influences of Recent Geodynamics

The method of determination of elastic moduli of the geological section rocks had been developed in real conditions. The method is based on application of non-classically linearized theory of elastic waves＇ propagation in the deformable media and utilization of neural networks when creating the geoseismic model. It is proposed to forecast the thin-layer model of medium by velocities of the shear waves on the base of seismic inversion of 2D profile by neural networks and geophysical well logging data. The method had been tested on materials of geophysical well logging data and 2D seismic profile related to one of the structures in the South-Caspian depression. The specific results for Poisson coefficient and elastic moduli of the third order had been obtained. The mentioned method can also be applied to forecast of other physical-mechanical properties of the medium.